The present invention relates to a toner used in an image forming method utilizing electrophotography, electrostatic recording, electrostatic printing or a recording method utilizing toner jet recording, and a resin composition for the toner.
Hitherto, a large number of electrophoto-graphic processes have been known, inclusive of those disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. In these processes, in general, an electrostatic latent image is formed on a photosensitive member comprising a photoconductive material by various means, then the latent image is developed with a toner, and the resultant toner image is, after being transferred onto a transfer material such as paper etc., via or without via an intermediate transfer member, as desired, fixed by heating, pressing, or heating and pressing, or with solvent vapor to obtain a copy or print carrying a fixed toner image.
As for the step of fixing the toner image onto a sheet material such as paper which is the final step in the above process, the most popular fixing method is a heating and pressing fixation system using hot rollers.
In the heating and pressing system, a sheet carrying a toner image to be fixed (hereinafter called xe2x80x9cfixation sheetxe2x80x9d) is passed through hot rollers, while a surface of a hot roller having a releasability with the toner is caused to contact the toner image surface of the fixation sheet under pressure, to fix the toner image. In this method, as the hot roller surface and the toner image on the fixation sheet contact each other under a pressure, a very good heat efficiency is attained for melt-fixing the toner image onto the fixation sheet to afford quick fixation.
In the fixing step, however, a hot roller surface and a toner image contact each other in a melted state and under a pressure, so that a part of the toner is transferred and attached to the fixing roller surface and then re-transferred to a subsequent fixation sheet to soil the fixation sheet. This is called an offset phenomenon.
Hitherto, as toner binder resins, polyester resins, and vinyl copolymers, such as styrene copolymers, have been principally used.
A polyester resin provides an excellent low-temperature fixability but is accompanied with a difficulty that it is liable to cause the high-temperature offset. For alleviating the difficulty, it has been tried to increase the viscosity of a polyester resin by increasing the molecular weight. In this case, however, the low-temperature fixability is liable to be impaired, and the pulverizability during toner production can also be impaired, thus providing a binder resin not suitable for production of smaller particle size toners.
A vinyl copolymer, such as a styrene copolymer, has excellent pulverizability suitable for toner production, and provides excellent anti-high-temperature offset performance because the molecular weight thereof can be increased easily. However, if the molecular weight is lowered in order to provide an improved low-temperature fixability, the anti-blocking property and developing performance are liable to be impaired.
In order to effectively utilize the advantages and compensate for the difficulties of the above two types of resins, several proposals have been made regarding the use of mixtures of these resins.
For example, Japanese Laid-Open Patent Application (JP-A) 54-114245 discloses a toner containing a mixture of a polyester resin and a vinyl copolymer. However, since a polyester resin and a vinyl copolymer essentially have poor mutual solubility, it is difficult to provide a toner satisfying low-temperature fixability, anti-high-temperature offset performance and anti-blocking property in combination unless a suitable mixing ratio of the resin is set.
Further, it is difficult to sufficiently improve a dispersibility of internal additives, such as a colorant and a wax, added for toner production, thus being liable to result in a problem in developing performance of the resultant toner. This difficulty is liable to be noticeable especially in production of smaller-particle size toners which are preferred in recent years.
JP-A 56-116043 and JP-A 58-159546 disclose a toner containing a polymer obtained by polymerizing a vinyl monomer in the presence of a polyester resin.
JP-A 58-102246 and JP-A 1-156759 disclose a toner containing a polymer obtained by polymerizing vinyl monomers in the presence of an unsaturated polyester.
JP-A 2-881 discloses a toner containing a polymer obtained by esterifying a polyester resin and a styrene-based resin having a specific acid value.
In the above-mentioned toners, the polyester resin and the vinyl copolymer can have an improved mutual solubility. However, it is difficult to uniformly disperse a wax added for toner production. The resultant toner still has room for improvement with respect to not only low-temperature fixability but also developing performance.
JP-A 4-338973 discloses a toner containing two species of polyester resins different in softening point and JP-A 8-166688 discloses a toner containing two species of polyester resins different in molecular weight.
Both of these toners, however, an anti-high-temperature offset performance of the resultant toner is at a level within that in the case of using an ordinary polyester resin, thus still having room for improvement.
JP-A 8-54754 discloses a toner containing a resin obtained by mixing a polyester with a specific resin prepared through addition polymerization of a vinyl monomer and polycondensation of monomers for a polyester resin performed in parallel with each other.
JP-A 8-44108 discloses a toner containing two species of specific resins different in softening point each prepared through addition polymerization of a vinyl monomer and polycondensation of monomers for a polyester resin performed in parallel with each other.
However, these toners fails to control a balance of crosslinking degree between a lower-molecular weight component and a higher-molecular weight component, thus still leaving room for improvement with respect to low-temperature fixability, dispersibility of wax, and developing performance for a long period.
U.S. Pat. No. 5,976,752 discloses a toner containing at least a binder resin, a colorant and a wax and the binder resin comprises a polyester resin, a vinyl resin, and a hybrid resin component comprising a polyester unit and a vinyl polymer unit. This toner is specified in term of THF (tetrahydrofuran) soluble and insoluble contents, ethyl acetate-soluble and -insoluble contents, chroloform-soluble and -insoluble contents, and a GPC (gel permeation chromatography) molecular weight distribution for a THF-soluble content. This toner exhibits a good low-temperature fixability and excellent anti-offset characteristic, anti-blocking characteristic and continuous image forming performance on a large number of sheets.
However, in order to further improve the low-temperature fixability while retaining the anti-offset characteristic, the anti-blocking characteristic and the continuous image forming performance, the toner has room for further improvement.
A generic object of the present invention is to provide a toner for developing electrostatic images having solved the above-mentioned problems.
A more specific object of the present invention is to provide a toner capable of exhibiting excellent low-temperature fixability and anti-high-temperature offset property and providing a good developing performance for a long period.
Another object of the present invention is to provide a toner wherein a wax is uniformly dispersed in a binder resin.
A further object of the present invention is to provide a resin composition for a toner as described above.
According to the present invention, there is provided a toner, comprising: at least a binder resin, a colorant and a wax, wherein
the binder resin has been formed from monomers including a vinyl monomer and polyester-forming monomers containing at least a polybasic carboxylic acid having three or more carboxyl groups or its anhydride, and comprises at least a hybrid resin comprising a vinyl polymer unit and a polyester unit,
the toner contains a THF (tetrahydrofuran)-soluble content which includes a first component having molecular weights of below 1xc3x97104 containing W1 (mol. %) of the polybasic carboxylic acid and its anhydride based on the polyester-forming monomers contained in the first component and a second component having molecular weight of at least 1xc3x97104 containing W2 (mol. %) of the polybasic carboxylic acid and its anhydride based on the polyester-forming monomers contained in the second component, W1 and W2 satisfying the following relationship:
0xe2x89xa6W1 less than 30,
0 less than W2 less than 50, and 
W2 greater than W1,
the THF-soluble content provides a GPC (gel permeation chromatography) chromatogram including 40-70 wt. % (M1) of a component having molecular weights of below 1xc3x97104, 25-50 wt. % (M2) of a component having molecular weights of 1xc3x97104-5xc3x97104, 2-25 wt. % (M3) of a component having molecular weights of above 5xc3x97104, and below 10 wt. % (M4) of a component having molecular weights of at least 10xc3x97104, M1, M2 and M3 satisfying the following relationship:
M1xe2x89xa7M2 greater than M3.
According to the present invention, there is also provided a resin composition for a toner, comprising:
at least a hybrid resin comprising a vinyl polymer unit and a polyester unit,
wherein the resin composition has been formed from monomers including a vinyl monomer and polyester-forming monomers containing at least a polybasic carboxylic acid having three or more carboxyl groups or its anhydride,
the resin composition contains a THF (tetrahydrofuran)-soluble content which includes a first component having molecular weights of below 1xc3x97104 containing w1 (mol. %) of the polybasic carboxylic acid and its anhydride based on the polyester-forming monomers contained in the first component and a second component having molecular weight of at least 1xc3x97104 containing w2 (mol. %) of the polybasic carboxylic acid and its anhydride based on the polyester-forming monomers contained in the second component, w1 and w2 satisfying the following relationship:
0xe2x89xa6w1 less than 30,
0 less than w2 less than 50, and
w2 greater than w1,
the THF-soluble content provides a GPC (gel permeation chromatography) chromatogram including 40-75 wt. % (m1) of a component having molecular weights of below 1xc3x97104, 23-45 wt. % (m2) of a component having molecular weights of 1xc3x97104-5xc3x97104, 2-25 wt. % (m3) of a component having molecular weights of above 5xc3x97104, and below 13 wt. % (m4) of a component having molecular weights of at least 10xc3x97104, m1, m2, and m3 satisfying the following relationship:
m1xe2x89xa6m2 greater than m3.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention.